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Terms starting with B

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Plasma Physics

Bohm Sheath Criterion

A fundamental boundary condition stating that positive ions entering a non-neutral plasma sheath must enter with a velocity at or exceeding…

v_ion ≥ c_s = √(k_B T_e / m_i) (at Sheath Entrance) m/s (Ion Acoustic Sound Speed c_s)
Quantum & Atomic Physics

Bohr Model

An early semi-classical atomic model proposing that electrons orbit the atomic nucleus only in discrete stationary orbits with quantized…

L = m v r = n ℏ, E_n = -13.6 eV / n² eV (Energy), m (Orbit Radius)
Foundations of Physics

Boltzmann Constant

The fundamental constant that converts thermodynamic temperature into microstate kinetic energy per particle.

k = R / Na = 1.380649 × 10⁻²³ J/K J/K
Biophysics & Medical Physics

Bone Mechanics

The study of mechanical structural behavior, anisotropy, and remodeling of bone tissue under physical loads.

Stress σ = F / A, Young's Modulus E_cortical ≈ 18 GPa MPa / GPa (Tensile & Compressive Strength)
Plasma Physics

Bootstrap Current

A self-generated toroidal electric current in a tokamak plasma driven by trapped particle banana orbits in steep pressure gradients.

I_bootstrap ∝ √ε (k_B / B_poloidal) (dn / dr) MA (Plasma Current Fraction)
Quantum & Atomic Physics

Bose-Einstein Condensate (BEC)

A state of matter formed by bosons cooled close to absolute zero, where a macroscopic fraction of particles collapse into the lowest…

T_c = (2 π ℏ² / (m k_B)) (n / ζ(3/2))^(2/3) nK (Nanokelvin Temperatures)
Quantum & Atomic Physics

Bosons

Subatomic particles possessing integer intrinsic spin that obey Bose-Einstein statistics and do not obey the Pauli Exclusion Principle.

Spin = 0, 1, 2... Dimensionless Particle Class
Mathematical & Computational Physics

Boundary Value Problem

A differential equation together with a set of additional constraints, called boundary conditions, specified at the boundaries of the…

Dirichlet: y(a)=y_A; Neumann: y'(a)=y'_A; Robin: α y(a) + β y'(a) = γ Differential Equation Condition
Thermodynamics & Statistical Physics

Boyle's Law

An ideal gas law stating that pressure is inversely proportional to volume at constant temperature.

P1 V1 = P2 V2 (at constant T) Pa·m³
Biophysics & Medical Physics

Brachytherapy

An internal radiation therapy technique where sealed radioactive sources are placed directly inside or adjacent to a tumor.

Inverse Square Dose Falloff: D(r) ∝ 1 / r² Gy/h (High or Low Dose Rate)
Quantum & Atomic Physics

Bragg's Law

The mathematical condition for constructive interference of waves scattered from parallel atomic lattice planes in a crystal.

n λ = 2 d sin θ m or nm (Wavelength and Spacing)
Nuclear & Particle Physics

Breeder Reactor

A specialized nuclear reactor designed to generate more fissile nuclear fuel than it consumes during operation.

²³⁸₉₂U + ¹₀n → ²³⁹₉₂U → ²³⁹₉₃Np → ²³⁹₉₄Pu (Breeding Ratio > 1) Breeding Ratio (Fissile Output / Input)
Plasma Physics

Bremsstrahlung Radiation in Plasma

Continuous electromagnetic radiation emitted when free plasma electrons undergo deceleration scattering off positive ions.

P_brems ∝ Z_eff n_e² √T_e W/m³ (Radiated Power Density)
Optics

Brewster's Law

The law stating that reflected light is 100% linearly polarized when the angle of incidence equals the polarizing angle, where reflected…

tan θ_p = n2 / n1 Degrees (°)
Condensed Matter & Materials Physics

Brillouin Zone

The uniquely defined fundamental primitive cell in reciprocal wavevector k-space containing all unique electronic and vibrational wave…

First BZ: Wigner-Seitz cell in reciprocal lattice space m⁻¹ (Reciprocal Wavevector k)
Astrophysics, Cosmology & Relativity

Brown Dwarf

A substellar object intermediate in mass between giant gas planets and low-mass stars, incapable of sustaining stable core hydrogen fusion.

13 M_J ≤ M < 80 M_J (~0.013 to 0.08 M_☉) Jupiter Masses (M_J) or M_☉
Thermodynamics & Statistical Physics

Brownian Motion

The random, erratic wandering movement of microscopic particles suspended in a fluid caused by relentless collisions with fast-moving fluid…

⟨x²⟩ = 2 D t, D = kB T / (6 π η r)
Condensed Matter & Materials Physics

Bulk Modulus

A mechanical material property measuring a solid or fluid's resistance to uniform volumetric compression under applied hydrostatic pressure.

K = -V (dP / dV) Pa or GPa (Gigapascals)
Classical Mechanics

Buoyancy

The net upward fluid force exerted on an object immersed in a fluid due to pressure difference between top and bottom.

Fb = ρ_fluid V_submerged g N
Plasma Physics

Burning Plasma & Alpha Heating

The state of a fusion plasma where thermal heating from 3.5 MeV alpha particles produced in Deuterium-Tritium fusion reactions becomes the…

P_alpha / P_heating ≥ 50% (Burning Plasma Condition Q ≥ 10) MW (Alpha Particle Heating Power)